Method of and apparatus for ascertaining at least one characteristic of a substance

ABSTRACT

At least one characteristic, such as the mass/density and/or moisture content and/or dielectric constant, of a substance (such as the rod-like tobacco filler of a continuously advancing cigarette rod or a continuously advancing rod-like filler of filter material for tobacco smoke) is ascertained by an evaluating circuit receiving high-frequency signals from a resonator arrangement which receives microwave signals at least at two different frequencies from one or more microwave generators. The substance is caused to advance through a dielectric resonator of the resonator arrangement, and the high-frequency signals are influenced by the substance. For example, the circuit can compare first and second curves of high-frequency signals which respectively are and are not influenced by a selected substance; the curves can have sloping flanks and each of the two frequencies can be allocated to a sloping flank of a curve. The circuit compares the amplitudes of the curves to ascertain the extent of damping of the output signals due to the presence of a substance at the resonator.

CROSS-REFERENCE TO RELATED CASE

This is a continuation-in-part of commonly owned copending patentapplication Ser. No. 08/799,129 filed Feb. 13, 1997 by Henning MOLLER,Jorg TOBIAS and Andreas NOACK for "METHOD OF AND APPARATUS FORASCERTAINING AT LEAST ONE CHARACTERISTIC OF A SUBSTANCE".

BACKGROUND OF THE INVENTION

The invention relates to improvements in methods of and in apparatus forascertaining one or more characteristics of certain substances, such astobacco. More particularly, the invention relates to improvements inmethods of and in apparatus for ascertaining one or more characteristics(such as the mass per unit length and/or the moisture content) of massflows of particulate materials, such as fragments of tobacco leaflaminae and/or other smokable substances.

It is already known to ascertain certain characteristics of mass flowsof tobacco particles by evaluating the extent of detuning, due to thepresence of such substances, of a high-frequency resonator whichreceives microwaves from a suitable generator and transmitshigh-frequency signals to a suitable evaluating circuit. The extent ofshift of the resonance frequency and damping of such high-frequencysignals (in comparison with output signals which are transmitted in theabsence of mass flows within the range of the high-frequency resonator)is indicative of the characteristic(s) of the material of the mass flow.

The making of smokers' products, such as plain or filter cigarettes,normally involves a testing of the mass flow of tobacco particles whichare to form the rod-like fillers of such products. As a rule, thetesting involves a determination of the mass of tobacco per unit lengthof the mass flow and/or the moisture content of the particles in themass flow and/or the dielectric constant of tobacco (as used herein, theterm "tobacco" is intended to embrace natural, reconstituted andartificial (substitute) tobacco). An accurate determination of the massper unit length and of the moisture content is particularly important inconnection with the making of cigarettes or other rod-shaped smokers'products (hereinafter referred to as cigarettes for short). For example,once the percentages of dry ingredients and moisture in a mass flow oftobacco particles are known, one can accurately determine the overallmass of the tested substance by simple addition of the signals denotingthe dry mass and the moisture content. The situation is similar inconnection with the processing of certain other substances such asfoodstuffs, chemicals, textile materials, paper and many others.

German patent No. 40 04 119 discloses the determination of the moisturecontent of substances in a cavity resonator which is connected to amicrowave generator. The patented apparatus resorts to a calibrationcurve to ascertain the resonance frequency and the half intensity widthof the resonance line.

OBJECTS OF THE INVENTION

An object of the invention is to provide a novel and improved method ofrapidly and accurately ascertaining one or more characteristics ofvarious substances, such as fragments of tobacco in a mass flow oftobacco particles in a production line for the making of rod-shapedsmokers' products.

Another object of the invention is to provide a method which can beresorted to for rapid and accurate determination of various ingredients(such as dry mass and/or wet mass) in mass flows of particulatematerials of the type being utilized in the tobacco processing, textile,paper making, chemical, food processing and other industries.

A further object of the invention is to provide method of ascertainingone or more characteristics of mass flow of filter material for tobaccosmoke.

An additional object of the invention is to provide method of rapidlyand accurately ascertaining one or more characteristics (such as thepercentages of solid and liquid ingredients, the total mass and/or thedielectric constant) of a rapidly advancing stream or flow of tobacco orfilter material in a cigarette making machine.

Still another object of the invention is to provide a method of in linedetermination of one or more characteristics of smokable materials,filter materials for tobacco smoke and/or other materials which arebeing conveyed in the form of mass flows or streams or rods or fillersin various plants of the tobacco processing industry.

A further object of the invention is to provide a novel and improvedapparatus for the practice of the above outlined method.

Another object of the invention is to provide a machine or productionline which embodies one or more apparatus for the practice of the aboveoutlined method.

An additional object of the invention is to provide the apparatus withnovel and improved means for transmitting signals to a resonatorarrangement of the above outlined apparatus.

Still another object of the invention is to provide the apparatus withnovel and improved means for processing signals being transmitted by theresonator arrangement of the above outlined apparatus.

A further object of the invention is to provide an apparatus which canbe utilized with advantage in modern high-speed production lines for themass-manufacture of plain or filter cigarettes, cigars, cigarillos,cheroots and/or other rod-shaped products of the tobacco processingindustry.

Another object of the invention is to provide an apparatus which can bedesigned to accurately and rapidly ascertain one or more characteristicsvarious substances, such as the dry mass, the moisture content, thetotal mass and/or the dielectric constant of tobacco particles or filtermaterial for tobacco smoke, in cigarette makers, filter rod makers orother types of production lines.

SUMMARY OF THE INVENTION

One feature of the present invention resides in the provision of amethod of ascertaining at least one characteristic of a substance byresorting to a high-frequency resonator arrangement which is detuned inthe presence of the substance. The method comprises the steps ofsupplying or transmitting to an input of the resonator arrangementmicrowaves having at least two different frequencies whereby an outputof the resonator arrangement respectively furnishes or transmits firstand second curves of high-frequency output signals in the presence andabsence of a substance at the resonator arrangement. Such curves havedifferent amplitudes, and the method further comprises the step ofevaluating the output signals including comparing the curves toascertain shifts of resonance frequencies of the output signals due tothe presence of a substance at the resonator arrangement and comparingthe amplitudes of the curves to ascertain damping of output signals dueto the presence of a substance at the resonator arrangement.

The supplying step can include continuously transmitting to the input ofthe resonator arrangement microwaves having at least two differentfrequencies.

The method can further comprise the step of periodically varying thefrequencies of microwaves which are being transmitted to the input ofthe resonator arrangement. This varying step can include repeatedlyshifting between higher and lower frequency values. Such varying stepcan also include repeatedly and continuously wobbling betweenhigher-frequency and lower-frequency values. The frequencies of themicrowaves can be allocated to a sloping flank of a curve ofhigh-frequency output signals. The wobbling step can involvesubstantially sinusoidally wobbling the frequencies of the microwavesbetween threshold values with relatively small frequency changes ordifferences. The output signals can have d-c fractions and substantiallysinusoidally varying a-c fractions. The evaluating step of such methodcan comprise transmitting the d-c fractions and the a-c fractions todiscrete calculating or computing stages, polynomially computing thefractions in the respective stages with constants to thus generatepartial signals, and adding or summing the partial signals. Suchevaluating step can further comprise ascertaining the constants byparameterization on the basis of reference values of the substance; suchreference values can include--as a function of the at least onecharacteristic to be ascertained in accordance with the novel method--atleast one of the density/mass, moisture content and dielectric constantof the substance being tested.

The aforementioned threshold values can be at least substantiallysymmetrical with reference to an inversion point of a downwardly slopingflank of a curve.

The at least two different frequencies of microwave signals can besymmetrical with reference to a resonance frequency which is notinfluenced by the substance being tested, and the at least two differentfrequencies can be allocated to downwardly sloping flanks of a resonancecurve.

The method can further comprise the step of generating the microwaves,and such step can include substantially sinusoidally modulating theamplitude of a microwave oscillation at a relatively low frequency. Themodulating step can include maintaining the basic frequencies of thedeveloping frequency bands at a downwardly sloping flank of the curve,preferably or particularly at an inversion point of such flank.

The supplying step can also include transmitting to the input of theresonator arrangement microwaves at two modulation-establishedfrequencies, and the evaluating step of such method can comprise scalingdown the microwave frequencies and selectively filtering those frequencyranges which influence the shifts of resonance frequencies and thedamping of the output signals.

The substance can consist of or it can contain tobacco, and the at leastone characteristic to be ascertained is or can be the mass/density oftobacco.

The substance to be tested can be tobacco in a tobacco particle flow,and the at least one characteristic to be tested can be the moisturecontent/mass of tobacco. The substance to be tested can contain or canconstitute tobacco in a flow of shredded and/or otherwise comminuted(cut) tobacco particles, and the at least one characteristic to beascertained can be the dielectric constant of cut or comminuted orshredded tobacco.

Another feature of the invention resides in the provision of anapparatus for ascertaining at least one characteristic of a substance(e.g., tobacco). The apparatus comprises a resonator arrangement, andmeans for supplying to an input of the resonator arrangement microwavesignals at least at two different frequencies. The resonator arrangementhas output means for the transmission of first and second high-frequencysignals which are respectively generated in the presence and in theabsence of a substance to be tested at the resonator arrangement, andthe apparatus further comprises means for evaluating the firsthigh-frequency signals. The evaluating means comprises means forcomparing first and second resonance curves having different amplitudesand respectively denoting the first and second high-frequency signals tothus ascertain shifts of resonance frequency attributable to thepresence of a substance to be tested at the resonator arrangement, andmeans for comparing the amplitudes of the first and second resonancecurves to thus ascertain the damping of such amplitudes by a substanceto be tested.

The means for supplying microwave signals can include at least onemicrowave generator which is designed to uninterruptedly transmit to theinput of the resonator arrangement microwave signals at the at least twodifferent frequencies. The generator can include means for periodicallyaltering the frequency of the microwave signals.

The means for supplying microwave signals can be designed in such a waythat it comprises a microwave generator which is connected to the inputof the resonator arrangement and a frequency regulator which isconnected with the microwave generator to periodically vary thefrequency of signals from the microwave generator between higher andlower values.

Alternatively, the means for supplying microwave signals can comprise amicrowave generator which is connected to the input of the resonatorarrangement and a frequency regulator which is connected with thegenerator to continuously and regularly vary the frequency of signalsfrom the generator between higher and lower values.

The at least two different frequencies can be symmetrical to each otherwith reference to a resonance frequency of the second curve and arelocated at downwardly sloping flanks of the second curve.

It is also possible to design the means for supplying microwave signalsin such a way that it comprises a microwave generator connected to theinput of the resonator arrangement and a frequency regulator connectedwith the generator to continuously and regularly vary the frequency ofsignals from the generator between higher and lower values. Themicrowave signals are allocated to downwardly sloping flanks of at leastone of the curves. The frequency regulator can be arranged tosubstantially sinusoidally vary the frequency of signals from themicrowave generator. The comparing means of the evaluating means cancomprise means for ascertaining d-c and a-c fractions of the firsthigh-frequency signals.

The means for supplying microwave signals can include means fortransmitting to the input of the resonator arrangement microwaves atfrequencies having upper and lower threshold values and continuouslywobbling between such values. The threshold values are at leastsubstantially symmetrical to each other with reference to an inversionpoint of a downwardly sloping flank of a resonance curve.

The evaluating means can comprise calculating or computing circuits orstages which respectively receive d-c fractions and a-c fractions of thehigh-frequency signals and include means for polynomially computing orcalculating the fractions with constants to thus generate partialsignals, and means for summing or adding such partial signals. Suchevaluating means can further comprise means for ascertaining theconstants by parameterization on the basis of reference values of asubstance. The reference values can include--as a function of the atleast one characteristic to be ascertained by the improved apparatus--atleast one of the density/mass, moisture content and dielectric constantof the substance to be tested.

The means for supplying microwave signals can also comprise means forsubstantially sinusoidally modulating the frequencies of the microwavesignals with a relatively low frequency. Bands of modulated frequenciescan include a basic frequency at a downwardly sloping flank of theresonance curve, particularly or preferably at an inversion point ofsuch curve.

The resonator arrangement can comprise a preferably metallic housinghaving an inlet and an outlet for a flow of a substance to be tested(e.g., a tobacco stream). The housing can be dynamically balanced; forexample, such dynamically balanced housing can include or constitute acylinder. The resonator arrangement can further comprise at least onedielectric resonator in the housing, and such resonator can provide apath for the advancement of a substance (e.g., a cigarette rod) betweenthe inlet and the outlet of the housing. The resonator arrangement canfurther comprise a tubular guide for the substance, and such guide caninclude portions at the inlet and at the outlet of the housing. Apresently preferred guide extends through the at least one dielectricresonator. The just described resonator arrangement can further compriseconductive sleeves which surround the guide in the regions of the inletand the outlet of the housing; such sleeves can contain or they canconsist of a metallic material.

Alternatively, the resonator arrangement of the improved apparatus cancomprise two resonators each of which receives microwave signals fromthe supplying means, one of which transmits the aforementionedhigh-frequency signals, and the other of which transmits to theevaluating means additional signals which are influenced by a referencesubstance to compensate for disturbances. Such resonator arrangement canfurther comprise at least substantially identical housings for the tworesonators.

The at least one characteristic which is to be ascertained by theimproved apparatus can be the density/mass of tobacco or the moisturecontent of cut tobacco in a cigarette rod or the dielectric constant ofcut tobacco, particularly in a cigarette rod.

A further feature of the invention resides in the provision of a methodof ascertaining at least one characteristic of a substance by means of ahigh-frequency resonator arrangement which is detuned in the presence ofthe substance to be tested. This method comprises the steps of supplyingto an input of the resonator arrangement microwaves having twofrequencies whereby an output of the resonator arrangement respectivelyfurnishes first and second curves of high-frequency output signals inthe presence and absence of a substance (the curves have amplitudes andsloping flanks and each of the two frequencies is allocated to a slopingflank of a curve), and evaluating the output signals including comparingthe curves to ascertain shifts of resonance frequencies of the outputsignals due to the presence of a substance, and comparing the amplitudesof the curves to ascertain damping of output signals due to the presenceof a substance. The just outlined method can further comprise the stepof periodically varying the frequencies of the microwaves which aresupplied to the input of the resonator arrangement, and the varying stepof such method can include repeatedly switching between higher and lowerfrequency values.

Still further, the just outlined method can comprise the step ofmodulating the frequencies of the microwaves with a lower-frequencyrectangular a-c voltage. The output signals can constitute d-c signalsand the method can further comprise the steps of ascertaining those d-csignals which are transmitted by the output of the resonator arrangementat the minimum and maximum values of the modulated frequencies, andprocessing the thus ascertained maximal and minimal signals intoevaluation signals. The processing step can include providing a furthersignal which denotes the sum of the maximal and minimal signals andprocessing the further signal into a signal denoting an average value ofthe maximal and minimal signals. Such processing step can furtherinclude providing an additional signal which denotes the differencebetween the maximal and minimal signals, transmitting the further andadditional signals to discrete calculating stages, polynomiallycomputing the maximal and minimal signals in the respective stages withconstants to thus generate partial signals, and adding (summing up) thepartial signals. Such method can further comprise the step ofascertaining the aforementioned constants by parameterization on thebasis of those reference values of the substance which are to beascertained. Such reference values can include the density/mass, themoisture content and the dielectric constant of the substance to betested.

The substance to be tested can be tobacco, and the at least onecharacteristic can be the mass/density of tobacco. For example, thesubstance can constitute a rod-like filler of cut tobacco.Alternatively, the at least one characteristic can be the moisturecontent of tobacco, for example, the moisture content of successiveincrements of a rod-like filler of cut tobacco.

Still another feature of the invention resides in the provision of anapparatus for ascertaining at least one characteristic of a substance.The apparatus comprises a resonator arrangement, means for supplying toan input of the resonator arrangement microwave signals at twofrequencies (the resonator arrangement has output means for thetransmission of first and second high frequency signals which arerespectively generated in the presence and in the absence of a substanceat the resonator arrangement), and means for evaluating the firsthigh-frequency signals. The evaluating means comprises means forcomparing first and second resonance curves having amplitudes andsloping flanks. Each of the frequencies is allocated to a sloping flankof a curve and the first and second curves respectively denote the firstand second high-frequency curves to thus ascertain shifts of resonancefrequencies attributable to the presence of a substance at the resonatorarrangement. The evaluating means further comprises means for comparingthe amplitudes of the first and second resonance curves to thusascertain the damping of such amplitudes by a substance.

The supplying means of the just discussed apparatus can comprise amicrowave generator which is connected to the input, and a frequencyregulator which is connected with the generator to periodically vary thefrequency of signals from the generator between higher and lower values.

The apparatus can further comprise means for modulating the frequenciesof the microwaves with a lower-frequency rectangular a-c voltage. Thefirst and second high-frequency signals can constitute d-c signals, andthe modulated frequencies have maximum and minimum values. The apparatuscan further comprise means for ascertaining the d-c signals which aretransmitted by the output means of the resonator arrangement at theminimum and maximum values of the modulated frequencies, and means forevaluating the ascertained signals into evaluation signals. Theevaluating means can comprise summing and subtracting circuits havingoutputs for signals which are transmitted to discrete calculating stageshaving means for polynomially computing signals from the respective(summing, subtracting) circuits with constants to thus generate partialsignals. Such evaluating means can further comprise means for adding(totalizing) the partial signals as well as means for ascertaining theaforementioned constants by parameterization on the basis of referencevalues of a substance. The reference values can include (as a functionof the at least one characteristic to be ascertained) at least one ofdensity/mass, moisture content and dielectric constant of the substance.

The resonator arrangement can comprise a metallic housing having aninlet and an outlet for the flow of a substance to be tested, such as atobacco stream. The housing is or can be dynamically balanced and caninclude a cylinder. The resonator arrangement can comprise at least onedielectric resonator in the housing.

In accordance with one presently preferred embodiment, the at least onecharacteristic is the density/mass of tobacco and/or the moisturecontent of cut tobacco in a cigarette rod.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved apparatus itself, however, both as to its construction and themode of assembling, installing and utilizing the same, together withnumerous additional important features and advantages thereof, will bebest understood upon perusal of the following detailed description ofcertain presently preferred specific embodiments with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic partly elevational and partly sectional view ofan apparatus which is designed to ascertain one or more characteristicsof a continuous cigarette rod and is constructed and assembled inaccordance with a first embodiment of the invention;

FIG. 2 is a coordinate system showing the resonance curves of aresonator arrangement in the apparatus of FIG. 1, one curve beingindicative of the output signals when the dielectric resonator of theresonator arrangement is not influenced and the other curve beingindicative of the output signals when the resonator is influenced by asubstance to be tested;

FIG. 3 is a view similar to that of FIG. 1 but showing certain detailsof a modified apparatus wherein the resonator arrangement receiveswobbled microwave signals;

FIGS. 4a, 4b and 4c illustrate coordinate systems wherein the curvesdenote the high-frequency signals transmitted by the resonatorarrangement in the apparatus of FIG. 3;

FIG. 5 is a diagrammatic view of an evaluating circuit which can beutilized to ascertain the dry mass and/or the wet mass of successiveincrements of a rod-like tobacco filler which is confined in the tubularenvelope of a continuous cigarette rod;

FIG. 6 is a diagrammatic view of an evaluating circuit which is utilizedto furnish signals denoting the dielectric constants of successiveincrements of a flow of tobacco particles;

FIG. 7 is a diagrammatic view of a third apparatus wherein theevaluating circuit receives three signals having frequencies obtained asa result of modulation of a microwave signal;

FIG. 8 is a coordinate system showing a modulated microwave signal;

FIG. 9 is coordinate system similar to that of FIG. 2 but showing curvesdenoting the signals transmitted by the output means of the resonatorarrangement in the apparatus of FIG. 7;

FIG. 10 is a diagrammatic view similar to that of FIG. 1 but showing thedetails of still another apparatus with different means for transmittingmicrowave signals to the resonator arrangement and with different meansfor transmitting high-frequency signals to the evaluating circuit.

FIG. 11 is a diagrammatic view similar to that of FIG. 1 but showing thedetails of a further presently preferred apparatus;

FIGS. 12a, 12b and 12c illustrate coordinate systems wherein the curvesdenote the high-frequency signals transmitted by the resonatorarrangement in the apparatus of FIG. 11; and

FIG. 13 is a diagrammatic view of an evaluating circuit which can beutilized in the apparatus of FIG. 11.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring first to FIG. 1, there is shown an apparatus which is designedto ascertain at least one characteristic of a substance (tobacco)forming a rod-shaped filler 12b in a tubular envelope 12a of acontinuous rod 12, e.g., a rod containing fragments of tobacco leaflaminae in a cigarette paper wrapper and being ready to be subdividedinto plain cigarettes of unit length or multiple unit length. Forexample, the making of the rod 12 can take place in a machine known asPROTOS 100 which is distributed by the assignee of the presentapplication. PROTOS 100 is a high-performance production line with anoutput of 11000 cigarettes per minute or more.

The apparatus of FIG. 1 comprises a high-frequency resonator arrangement1 including a dielectric resonator 21 in a housing 2 which isdynamically balanced and can constitute a cylinder. The illustratedhousing 2 is made of a conductive metallic material, such as copper. Itis equally possible to employ other types of rotationally symmetricalhousings or housings having a polygonal cross-sectional outline and madeof a material other than copper or other than a metallic material.

The resonator arrangement 1 receives high-frequency signals (preferablymicrowave signals) from a source 3 (such as a generator) by way of afirst conventional coaxial cable 4, and a second conventional coaxialcable 6 is employed to connect the output of the resonator arrangement 1with an evaluating arrangement 11. The cables 4 and 6 are provided withcustomary coupling loops, not shown in FIG. 1.

The resonator 21 is made of a dielectric material, such as a ceramic ora synthetic plastic substance having a high dielectric constant (forexample, the resonator can be made of BaO--PbO--Nd₂ O₃ --TiO₂). Thisresonator is a hollow cylinder which is fixed in the housing 2 byresorting to suitable distancing or spacer means, not shown. A portion21a of the resonator 21 is movable axially of the other portion orportions, e.g., for the purpose of ascertaining and/or adjusting(selecting) the resonance frequency. An advantage of a dielectricresonator is that it contributes to higher sensitivity and greateraccuracy of measurements.

The housing 2 is provided with an inlet 7 and an outlet 9. This rendersit possible to insert a tubular guide 13 which defines a path for theadvancement of the cigarette rod 12 in the direction which is indicatedby an arrow 15. The apparatus of FIG. 1 is designed to ascertain the drymass and/or the wet mass and/or the overall mass or the dielectricconstant of the filler 12b. The guide 13 is made of a non-conductivematerial, such as quartz. One of the functions of the guide 13 is toprevent undesirable foreign matter (such as dust and small particles oftobacco) from penetrating into the housing 2; foreign matter in thehousing could interfere with proper operation of the resonatorarrangement 1. Tubular sleeves 14a and 14b surround the guide 13 in theregion of the inlet 7 and outlet 9 to prevent the radiation of excessivequantities of the high-frequency field from the housing 2 by way of theinlet and/or outlet. The sleeves 14a and 14b are preferably made of aconductive material, e.g., a suitable metallic material.

The axis 17 of the resonator 21 preferably coincides with the axes ofthe guide 13 and housing 2; such symmetrical arrangement of these partsalso contributes to the accuracy and reliability of the measurements.The sensitivity of the measurements is further enhanced due to the factthat the guide 13 extends through the central opening 20 of theresonator 21; such positioning of the parts 13 and 21 relative to eachother has been found to greatly enhance the sensitivity as well as theaccuracy of the determination of one or more parameters of the filler12b in the cigarette rod 12.

The cable 4 supplies to the dielectric resonator 21 two microwavesignals having different frequencies in the GHz range, e.g.,approximately 6 GHz. A conventional circulator 18 is employed to preventa feedback from the resonator arrangement 1 to the microwave generator3. FIG. 2 shows that the cable 4 supplies microwave signals havingfrequencies f1 and f2 which are symmetrical to each other with referenceto the resonance frequency fo (note the curve uo of FIG. 2 denoting theresonance frequency of the housing 2 when the guide 13 is empty). Themicrowave generator 3 is controlled by a frequency regulator 24 whichcauses the generator 3 to periodically shift from the transmission ofsignals having the lower frequency f1 to the transmission of signalshaving the higher frequency f2, back to the transmission oflower-frequency signals, and so forth.

It is also possible to employ two microwave generators in lieu of thesingle generator 3; the two generators are then designed to transmitsignals having slightly or somewhat different frequencies, and amodified frequency regulator then causes the two generators toalternately supply different-frequency signals via cable 4 and on to thehigh-frequency resonator arrangement 1. For example, the regulator whichis used in conjunction with two generators can be set up to turn off oneof the generators when the other generator is on, to thereupon shut offthe other generator while turning on the one generator, and so forth.

It is equally possible to supply (wobble) microwave signals which arefrequency modulated symmetrically relative to the resonance frequency foand to employ for the measurement only those signals which exhibit thefrequencies f1 and f2.

The cable 6 transmits output signals from the resonator arrangement 1,by way of a (feedback preventing) circulator 19 and on to a microwavediode 22. For example, the diode 22 can be that known as Type HP 8472Bwhich is distributed by Hewlett-Packard, Herrenberger Strasse 130,D-71034 Boblingen, Federal Republic Germany. The purpose of the diode 22is to convert the microwave signals into d-c signals. The signals U atthe output of the diode 22 are represented by the curve uo of FIG. 2when the guide 13 is empty, and by the curve u when the guide 13contains an advancing cigarette rod 12.

Since the frequencies f1 and f2 are symmetrical with reference to theresonance frequency fo, the signals U10 and U20 which are transmitted bythe diode 22 are identical, i.e., the difference between the signals U10and U20 (as measured along the ordinate in the coordinate system of FIG.2) is zero. Such situation prevails when the guide 13 is empty. When theapparatus of FIG. 1 is in use (i.e., when a cigarette rod 12 or anyother body to be tested in caused to advance through the guide 13), thevalues of the resonance frequency f are reduced and, furthermore, theamplitude is also reduced (reference should be had to the curve u ofFIG. 2). At the frequencies f1 and f2, the diode 22 then transmitssignals U1 and U2 having different values (as measured along theordinate). The difference between the signals U1 and U2 is dependent onthe extent of shift of resonance frequency, i.e., it increases inresponse to an increase of such shift. An evaluation of the signals atthe frequencies f1 and f2 renders it possible to ascertain the extent ofdamping and the extent of shift of resonance frequency. Thus, and thesame as in connection with other types of high-frequency measurements,the evaluating arrangement 11 can ascertain the mass/density ratio(independently of the moisture), the moisture (independently of thedensity) as well as the dielectric constant. If the correspondingsignals are added up (summed), one can ascertain the total massincluding the dry mass and the wet mass.

The connection between the output of the diode 22 and the input of theevaluating arrangement 11 comprises an analog-to-digital (A/D) converter23 (e.g., a circuit known as Type MX 7672-03 distributed by MaximIntegrated Products, 120 San Gabriel Drive, Sunnyvale, Calif. 94086).The circuit 23 digitalizes the signals from the diode 22 and furtherserves as a gate circuit which permits the signals from the diode 22 toreach the input of the evaluating arrangement 11 when it receives acorresponding signal from the frequency regulator 24 via conductor means25. The regulator 24 applies to the microwave generator 3 voltageimpulses of different intensities, and such signals influence thefrequencies of signals which are being transmitted via coaxial cable 4.As already explained above, the arrangement can be such that thegenerator 3 is caused to shift from the transmission of signals having alower frequency f1 to the transmission of signals having a higherfrequency f2, thereupon back to the transmission of signals having thefrequency f1, and so on.

In order to exclude transitional phenomena, the A/D converter 23receives signals to connect the output of the diode 22 with the input ofthe evaluating arrangement 11 only when the resonator arrangement 1actually receives (via cable 4) a signal having the frequency f1 or asignal having the frequency f2.

FIG. 3 illustrates a modified apparatus. Those component parts of themodified apparatus which are identical with or clearly analogous to thecorresponding component parts of the apparatus of FIG. 1 are denoted bysimilar reference characters. The microwave generator 3 is againdesigned to transmit microwave signals having a frequency in the GHzregion (e.g., about 6 GHz). A frequency regulator 24 is operativelyconnected with and causes the generator 3 to periodically vary thefrequency of output signals in a sinusoidal fashion. This can be readilyseen in FIG. 4a wherein the curve s denotes the changes of frequency fas a function of time t. The average frequency fm (for example, severalhundred KHz) is continuously varied sinusoidally (as indicated by thecurve s) within a frequency range Δf. As shown in FIG. 4b, the averagefrequency fm is preferably at the inversion point Uow of the resonancecurve uo which has been determined while the housing 2 of the resonatorarrangement 1 was empty. The output signal U of the diode 22, whichreceives signals from the generator 3 via circulator 18, resonatorarrangement 1 and circulator 19 fluctuates between the values Uomin andUomax when no tobacco is caused to pass through the housing 2 of theresonator arrangement 1. In actual use, i.e., when a filler 12b oranother flow of fibrous material of the tobacco processing industry iscaused to advance through the dielectric resonator in the housing of theresonator arrangement 1 of FIG. 3, the progress of the damping curve isthat shown in FIG. 4b, as at u, which exhibits the values Umin and Umax.The reference characters Uomit and Umit denote average values which areavailable at the average frequency fm. In FIG. 4b, the referencecharacter fo again denotes the resonance frequency when the housing ofthe resonator arrangement of FIG. 3 is empty, and the character fdenotes the resonance frequency when the apparatus of FIG. 3 is inactual use.

The coordinate system of FIG. 4c shows the variations of the signals Uat the output of the diode 22 of FIG. 3 as a function of time. When theapparatus of FIG. 3 is not in actual use, the corresponding curveincludes a d-c fraction Uog and an a-c fraction Uoa; however, the curvehas a d-c fraction Ug and an a-c fraction Ua when the apparatus is inactual use.

FIG. 3 shows that the signals at the output of the diode 22 aretransmitted to a d-c fraction filter 26 and to an a-c fraction filter27. The two filters 26 and 27 respectively transmit signals to A/Dconverters 28 and 29 wherein the corresponding signals are digitalizedprior to being transmitted to the corresponding inputs of the evaluatingarrangement 11. The latter can transmit (via conductor means 31) to thefrequency regulator 24 suitable correction signals as soon as theaverage frequency fm migrates beyond the inversion point of theresonance curve uo shown in FIG. 4b. Such correction via conductor means31 causes the frequency fm of the output signal from the generator 3 toreassume the value Uow which corresponds to the inversion point of theresonance curve Uo.

Based on a comparison between the d-c fractions Uog and Ug, as well asbetween the a-c fractions Uoa and Ua (when the housing 2 respectivelydoes not contain a filler 12b and contains such a filler), theevaluating arrangement 11 can draw conclusions regarding thecharacteristics of tobacco (such as its wet mass, its dry mass and/or isdielectric constant). This will be explained in detail with reference toFIGS. 5 and 6.

FIG. 5 shows schematically the processing of the signals Ua, Ug (seeFIG. 4c) in the evaluating arrangement 11 of the apparatus which isshown in FIG. 3 for the purpose of ascertaining the mass/density values.In the following description, the signal Ua is intended to denote thed-c value of the a-c fraction shown in FIG. 4c. The first step involvesthe storage of digitalized signals in the memories SUg and SUa which areshown in FIG. 5. Such signals are addressed by a scanner in a sequencecorresponding to predetermined increments of the cigarette rod 12, e.g.,increments each having a length of 1 mm. This means that, if thecigarette rod 12 is advanced at a rate required to turn out 10000 plaincigarettes of unit length (60 mm) per minute, the addressing or scanningfrequency is 100 microseconds. In other words, the memories SUg and SUaare addressed at intervals of 100 microseconds. The duration of thepulses Ig and Ia of transmission of signals (values) from the memoriesSUg and SUa to the calculating stages Rg and Ra, respectively, of theevaluating arrangement 11 is even less. In the stages Rg and Ra, thetransmitted signals are processed with constants to furnish outputvalues Ag and Aa, respectively. In a simple case, the processing ofsignals in the stages Rg and Ra can be carried out with polynomials ofthe type a+b Ug=Ag and c+d Ua=Aa, respectively. The constants a, b, cand d are ascertained by resorting to parameterizing, namely bymeasuring the values Ug and Ua of cigarettes which were weighed toaccurately ascertain their masses/densities. The relationships betweendifferent masses/densities and the corresponding values of Ug and Uarender it possible to ascertain the aforementioned constants.

In principle, it is equally possible to resort to polynomials of ahigher order or to other types of functions.

The signals Ag and Aa at the outputs of the respective calculatingstages Rg and Ra are transmitted to the corresponding inputs of a firstadding or summing circuit or stage Ad, and the signal Ae at the outputof the circuit Ad is indicative of the density/mass. If the intensityand/or other characteristic(s) of the signal Ae departs or depart fromthe desired or required characteristic or characteristics, a correctionstage Kg can be utilized to transmit an empirically determinedcorrection signal Ak to the corresponding input of a second adding orsumming circuit or stage Add which processes the signals Ae and Ak tofurnish an output signal Aed which is even more accuratelyrepresentative of the density/mass value of the filler 12b in the testedcigarette rod 12.

The evaluation of signals in the arrangement 11 of the apparatus whichis shown in FIG. 1 can be carried out in a manner analogous to the justdescribed mode of operation of the arrangement 11 in the apparatus ofFIG. 3. The signals furnished by the A/D converter 23 of FIG. 1 arestored in memories corresponding to the memories SUg, SUa of FIG. 5.

The evaluation with the evaluating circuit arrangement of FIG. 5 canalso be realized by employing a third memory SU3. The memories SUg=SU1and SUa=SU2 receive the signals U1, U2 (FIG. 7). The calculating stagesare denoted by the characters R1, R2, R3 and the signals at the outputsof these stages are respectively shown at r1, r2 and r3. Thetransmission or transfer pulses are respectively shown at I1, I2 and I3.

Basically, an evaluation of high-frequency measurement signals for thepurpose of ascertaining the moisture content of tobacco in a cigaretterod can be carried out in the same way as already described hereinabove.The difference is that, in lieu of utilizing cigarettes having a knownweight/mass, the parameterization involves the utilization of cigaretteshaving certain known moisture quantities or percentages, i.e., variousvalues of relative moisture.

FIG. 6 shows schematically the processing (evaluation) of signals Ua, Ug(reference should be had again to FIGS. 4a, 4b and 4c) in an evaluatingcircuit 11 of the type utilized in the apparatus of FIG. 3 for thepurpose of ascertaining the dielectric constant .di-elect cons. of thetobacco filler 12b in the cigarette rod 12. The first step involvestemporary storage of the signals Ug and Ua in the memories SUg and SUa.As already described with reference to FIG. 3, memories SUg and SUa areaddressed periodically and at relatively short time intervals, i.e., thecontents of these memories are transmitted by transmission or transferimpulses Ig and Ia to selected calculation or computing stages. Asshown, the real portion of the information stored in the memory SUg istransmitted to the stage R'g and the imaginary portion of suchinformation is transmitted to the stage R"g. Analogously, the realportion of the information obtained in the memory SUa is transmitted tothe stage R'a, and the imaginary portion of such information istransmitted to the stage R"a. The stages R'g and R'a process the realportions with constants into output signals E'g E'a, and stages R"g, R"aprocess the imaginary portions with constants into imaginary signalsE"g, E"a. Computing in the respective stages takes place withpolynomials the constants of which are determined by resorting to actualmeasurements of the real and imaginary parts of the dielectric constantsof sample cigarettes. Output signals E'g and E'a which correspond to thereal parts are transmitted to an adding or summing circuit or stage A'd,and the imaginary parts E"g and E"a are transmitted to a second addingor summing circuit A"d. The added signals .di-elect cons.' provide thereal part of the dielectric constant (at the output of the circuit orstage A'd) and the added signals .di-elect cons." provide the imaginarypart of the dielectric constant (at the output of the circuit or stageA"d). The reference character V denotes in FIG. 6 a conventional circuitwhich furnishes a complex value .di-elect cons. on the basis of thevalues 6'.di-elect cons. and .di-elect cons.".

A correction stage or circuit (corresponding to the stage Kg shown inFIG. 5) can be utilized to furnish, when necessary, empiricallydetermined correction signals. The value of the complex dielectricconstant .di-elect cons. can be ascertained (in V) by vectorial additionof the values .di-elect cons.' and .di-elect cons.".

FIGS. 7, 8 and 9 illustrate certain features of a further apparatusemploying a microwave generator 3 for the transmission of microwaves,preferably in the GHz range (for example, approximately 6 GHz). Thesignal from the generator 3 is transmitted as carrier frequency to amodulating circuit 36 wherein the microwave signal is amplitudemodulated with at least one substantially sinusoidal signal having aconsiderably lower frequency and being transmitted by a sender 37. Amodulator which can be utilized at 36 in the apparatus of FIG. 7 togenerate a secondary frequency signal by resorting to amplitudemodulation is known as Module MDC-177 and is distributed by the FirmAdams Russel, Anzac Division, 80 Cambridge Street, Burlington, Md.

A specific example of an acceptable modulating circuit 36 is as follows:5.8 GHz modulated with 10 MHz provides 5.790 GHz and 5.810 GHz. Asimilar or identical component part can be utilized in the apparatus ofFIG. 10 as a mixer 47 to effect a downward mixing of the GHz frequency.Example: The characteristic frequencies of 5.790 GHz and 5.810 GHz mixedwith 5.7850 GHz provide 25 MHz and 45 MHz.

The progress of an amplitude modulated microwave signal Umod is shown inthe coordinate system of FIG. 8 as a function of time t. It compriseshigh-frequency microwave oscillations u of the generator 3 and thesuperimposed modulating oscillation which forms a substantiallysinusoidal envelope curve h. The amplitude modulated microwave signal istransmitted, by way of the circulator 18 shown in FIG. 7, to a resonatorarrangement 1 and the high-frequency signals furnished by the outputmeans of the arrangement 1 are caused to pass through a furthercirculator 19 to the input e of a signal splitting or dividing circuit38, e.g., a circuit of the type known as Type HP Power Splitter 116678distributed by the Firm Hewlett-Packard, Herrenberger Strasse 130,D-71034 Boblingen, Federal Republic Germany. As shown in FIG. 9, theamplitude modulated signal furnishes (in the embodiment of FIG. 7) threefrequency bands, namely a basic frequency band f2 and two auxiliary orsecondary frequency bands f1 and f3. As concerns the resonance curve,the basic frequency band f2 for an empty resonator arrangement 1 ispreferably selected in such a manner that it is located at the inversionpoint Uw of the resonance curve uo. The corresponding signals U1, U2 andU3 on the resonance curve u of signals which are damped by a substancein the resonator arrangement 1 (the resonance frequency of the curve uhas been shifted due to the presence of the filler 12b in thearrangement 1) are ascertained in that an input signal furnished to theinput e of the signal dividing circuit 38 is split into three signalswhich are transmitted by the outputs a, b, c of the circuit 38 to threefilters 39a, 39b, 39c, respectively. These filters are set up in such amanner that each thereof permits the passage of a signal of a frequencyband f1, f2, f3. For example, the filters 39a, 39b, 39b can be of thetype known as MAX 274 distributed by Maxim Integrated Products, 120 SanGabriel Drive, Sunnyvale, Calif. 94086. The outputs of the filters 39a,39b, 39c are respectively connected to the inputs of diodes 22a, 22b,22c which transmit d-c signals, and such signals are digitalized by therespective ones of three A/D converters 41a, 41b, 41c. The outputs ofthe converters 41a, 41b, 41c are connected to the respective inputs ofthe evaluating or processing circuit 11 of FIG. 7.

In principle, it suffices to process two of the three ascertainedsignals (such as the signals U1, U2 or U1, U3 or U2, U3) of the dampedresonance curve u for the ascertainment of the wet mass or dry mass.However, it is also possible to carry out such determination byresorting to three signals. Furthermore, it is possible to form bymodulation more than two auxiliary or secondary bands and to thereuponevaluate the corresponding signals.

The apparatus of FIG. 7 can be modified in such a way that the averagefrequency f2 is not located at a flank of the resonance curve u (seeFIG. 9) but rather at its apex, i.e., at fo. In such apparatus, theauxiliary or secondary frequencies f1 and f2 are symmetrical thereto sothat the corresponding signals U1, U3 can be evaluated in a manner to bedescribed with reference to FIG. 10.

The apparatus of FIG. 10 also employs a generator 3 which transmitsmicrowave signals in the GHz frequency range. A modulator 36 is providedto modulate the signals from the generator 3 in a manner as alreadydescribed with reference to FIGS. 5 and 6; the input a of the circuit 36receives a modulating signal from a suitable source. The circuit 36transmits several microwave signals having frequencies which are closelyadjacent each other. Such signals are amplified at 46 and aretransmitted to the input of the resonator arrangement 1. As alreadydescribed with reference to FIGS. 1 and 2, the microwave signals whichare being transmitted to the input of the resonator arrangement 1 aresymmetrical to the resonance frequency for the idle (empty) resonatorarrangement 1. Basically, it is equally possible to employ two microwavegenerators in lieu of the single generator 3 of FIG. 10, and eachdiscrete generator transmits microwave signals at a selected frequencyother than the frequency of the signals transmitted by the othergenerator. The decoupling can take place in the same manner asdescribed, for example, with reference to FIG. 1, i.e., by resorting tocirculators 18 and 19 (not shown in FIG. 10).

The microwave signals are influenced by the presence of tobacco (such asshredded and/or otherwise cut tobacco particles in the filler 12b of acigarette rod 12) in the resonator arrangement 1 of FIG. 10, and thehigh frequencies of the thus influenced microwave signals areconsiderably reduced in the aforementioned mixer 47 having an input afor the reception of a suitable signal. Two selected characteristicsignals having considerably lower frequencies are transmitted to thediodes 22a, 22b by way of the respective filters 39a, 39b. The d-csignals at the outputs of the diodes 22a, 22b are digitalized in thecorresponding A/D converters 41a, 41b, and the thus obtained signals aretransmitted to the corresponding inputs of the evaluating circuit 11.The lowering of frequencies renders it possible to employ simpler andsharper filters for the selected frequency bands.

Signals which are transmitted by the microwave diodes (such as thediodes 22a-22c of FIG. 7 or the diodes 22a, 22b of FIG. 10) areinfluenced by the temperature of the tested material (such as tobacco).In accordance with the invention, such influence of the temperature canbe compensated for by ascertaining the temperature of the testedsubstance in any well known manner (for example, by employing atemperature sensor in the resonator arrangement 1). It is also possibleto utilize a temperature sensor upstream of the resonator arrangement 1,for example, in that part of a cigarette making machine or productionline where the cigarette rod 12 or the rod-like filler 12b is formed (anexample of such part of a production line is the so-called distributoror hopper of a cigarette maker). It is also possible to employ aninfrared radiation thermometer which is trained upon the ends ofcigarettes obtained as a result of severing of the cigarette rod 12 atregular intervals to turn out plain cigarettes of unit length ormultiple unit length. The thus obtained signals are utilized tocompensate for the influence of the temperature of the tested substanceupon the diode or diodes.

The resonator arrangement 1 can be heated to an appropriate temperatureto avoid the condensation of water.

In accordance with still another feature of the invention, a drift ofthe measuring or monitoring system can be compensated for by resortingto reference diodes or, if necessary, by utilizing an additionalresonator arrangement. For example, the apparatus can employ tworesonator arrangements having identical or substantially identicalhousings and a discrete dielectric resonator in each housing. The inputsof such discrete resonator arrangements are connected to suitable means(such as one or more microwave generators 3) for supplying microwavesignals.

Still further, it is within the purview of the invention to employ aresonator arrangement wherein the closed or substantially closedmetallic housing (such as the housing 2 of the arrangement 1 shown inFIG. 1) is replaced with an open housing having at least one part (e.g.,of a ceramic material) which is permeable to microwaves. Microwaves canpenetrate through such permeable part to enter into a flow or anotherbody of a substance to be tested, e.g., a flow of shredded and/orotherwise comminuted tobacco leaves. An advantage of such resonatorarrangements is that they can be utilized for the ascertainment of oneor more characteristics of a substance which need not be confined in anenvelope (such as the tubular wrapper 12a of the cigarette rod 12 shownin FIG. 1). The non-confined substance can be tested to ascertain one ormore characteristics, such as the mass/density and/or the moisturecontent and/or the dielectric constant of tobacco or other flowablesubstances.

An advantage of the improved method and apparatus is that they permitrapid and accurate determination of various characteristics of numeroussemiconducting substances, such as tobacco, particularly the wet massand/or dry mass and/or dielectric constant.

FIG. 11 shows a further apparatus wherein the frequency of an outputsignal furnished in the gigahertz range (e.g., about 6 GHz) by amicrowave generator 3 is periodically shifted between two values by afrequency regulator circuit 24. For example, one can employ arectangular a-c voltage of approximately 100 KHz. This can be seen inFIG. 12a which illustrates changes of the frequency f as a function oftime t. The median or average frequency fm is periodically varied withina frequency range Δf in accordance with a rectangular curve s, namelybetween a higher value f2 and a lower value f1.

The output signals which are transmitted by the microwave generator 3are supplied to a circulator 18 which prevents a feedback of the outputsignals and transmits such signals to a high-frequency (HF) resonatorarrangement 1, e.g., an arrangement of the type shown in and alreadydescribe with reference to FIG. 1. It is assumed that the resonatorarrangement 1 of FIG. 11 confines a length of a continuous cigaretterod, e.g., a rod of the type shown in FIG. 1 (as at 12). Such rodcomprises a tubular envelope surrounding a compacted rod-like filler ofsmokable material. However, it is equally possible to employ thehigh-frequency resonator arrangement 1 of FIG. 11 as a means formonitoring one or more characteristics of another substance, e.g., offilter material for tobacco smoke such as a rod-like filler of syntheticfibrous material within a tubular wrapper of paper, artificial cork orthe like. The details of the resonator arrangement 1 of FIG. 1 can matchthose of the similarly referenced resonator arrangement of FIG. 1.

As shown in FIGS. 12a and 12b, the average or median frequency fm of thesignals denoted by the rectangular curve s of FIG. 12a is preferablylocated at the inversion point of the resonance curve uo which wasascertained in the resonator arrangement 1, in the absence of tobacco orfilter material, for different frequencies of the supplied microwaves(from the source 3 via circulator 18). The progress of the resonancecurve s (when the resonator arrangement 1 confines a portion of anadvancing tobacco stream 12 shown in FIG. 1) is shown in FIG. 12b. Theresonance frequency when the resonator arrangement 1 is not beingtraversed by a continuous rod of confined tobacco or tobacco smokefiltering material is denoted by the curve uo of FIG. 12b, and the curveu denotes how the resonance frequency f1 develops when the resonatorarrangement 1 is actually traversed by a continuous wrapped filler oftobacco, filter material for tobacco smoke or the like. The resonancefrequency fo develops when the resonator arrangement 1 is empty, and theresonance frequency f develops when a wrapped rod-like filler (such as12 in FIG. 1) is caused to pass through the resonator arrangement 1.

The lower frequency value f1 on the rectangular curve s in thecoordinate system of FIG. 12a corresponds to the value denoted by thepoint Uof1 on the resonance curve uo (resonator arrangement 1 empty) ofFIG. 12b, and to the value denoted by the point Uf1 on the resonancecurve u (resonator arrangement 1 confining a length of an axiallyadvancing cigarette rod 12) of FIG. 12b. The upper frequency value f2 ofthe rectangular curve s shown in FIG. 12a corresponds to the valuesrespectively denoted by the points Uof2 and Uf2 on the curves uo and uof FIG. 12b. The values Uf1, Uf2, Uof1 and Uof2 are also shown in thecoordinate system of FIG. 12c.

The output signals of the resonator arrangement, namely the resonancesignals at the lower modulation value (f1) and the higher modulationvalue (f2), are transmitted to a resonance diode 22 by way of a secondcirculator 19 which prevents a feedback to the resonator arrangement 1.The diode 22 can be of the character known as Type HP/8472 B availableat Hewlett-Packard. The purpose of the diode 22 is to convert theincoming microwave signal into a d-c signal. The d-c signal istransmitted to a sensor 51 in response to signals from a synchronizer 52whose operation is a function of the rectangular a-c voltage supplied bythe frequency regulator 24. The regulation is carried out in such a waythat the voltage values of the resonator arrangement 1 are addressed atthe exact instants when the microwave generator 3 furnishes to theresonator arrangement 1 microwaves with the higher (f2) or lower (f1)frequency values of the rectangular curve s.

The above outlined mode of operation ensures that one can obtain thevalues Uf2 and Uf1 (FIGS. 12b and 12c) which are respectively stored inshort-term memories 53 and 54. The output signals of the memories 53 and54 are transmitted to a summing circuit 56 and to a subtracting circuit57. The circuit 56 establishes the value 1/2(Uf2+Uf1)=Ug, and thecircuit 57 establishes the value (Uf2-Uf1)=Ua (see also FIG. 12c). Thesignals or values Ug and Ua are transmitted to the corresponding inputsof the evaluating arrangement 11 the details of which are illustrated inFIG. 13 and which serves to ascertain, for example, the density/mass orthe moisture content of a continuously moving body of a substance, e.g.,a rapidly advancing cigarette rod containing a rod-like tobacco fillerwithin a tubular wrapper of cigarette paper or the like.

A specially designed circuitry can be provided to ensure that themicrowave generator 3 receives a correction signal from the evaluatingarrangement 11 via conductor means 31 as soon as the average frequencyfm (FIG. 12a) migrates beyond the inversion point of the resonance curveuo. The correction signal which is transmitted via conductor means 31ensures that the frequency fm at the output of the microwave generator 3is caused to reassume the value corresponding to the inversion point ofthe resonance curve uo.

The manner in which the signals Ua and Ug are processed in theevaluating arrangement 11 of FIG. 1 in order to ascertain themass/density value of the rod-like tobacco filler is shown in FIG. 13.The first step involves storing the signals Ua and Ug in digitalizedform in memories SUa and SUg. A readout device is provided to addressthe memories SUg and SUa in a sequence corresponding to selectedmovements of the cigarette rod passing through the resonator arrangement1 of FIG. 11. For example, each such movement can have a length of 1 mm.Thus, if the cigarette rod is transported through the resonatorarrangement at a speed which is required to produce 10000 cigarettes(each having a length of 60 mm) per minute, the scanning frequency is inthe range of 100 microseconds. In other words, the information which isstored in the memories SUg and SUa is addressed at a frequency of 100microseconds. The pulses Ig and Ia for the transmission of suchinformation to calculating stages Rg and Ra are even shorter than 100microseconds, and the stages Rg and Ra process the incoming signalstogether with constants to furnish output signals Ag and Aa entering thecorresponding inputs of a first summing or adding stage Ad. In a simplecase, the calculation in the stages Rg and Ra can be carried out withpolynomials of the type a+b Ug=AG and c+d Ua=Aa. The constants a, b, cand d are ascertained by resorting to parameterization involving aweighing of cigarettes to determine the exact values of mass/density andthe related values of Ug and Ua. The relationships between variousdensities/masses and the corresponding values of Ug and Ua permit adetermination of the constants a to d.

In principle, it is equally possible to employ higher-order polynomialsand/or other functions.

The output signals Ag and Aa are transmitted (by the calculating stagesRg and Ra) to the first summing or adding stage Ad which transmits anoutput signal Ae denoting the mass/density of the monitored substance.If the output signal Ae deviates from the exact (e.g., measured) valueof the mass/density, one can employ a correction stage Kg whichtransmits an empirically ascertained correction signal Ak to a secondadding or summing stage Add which further receives output signals Aefrom the first summing or adding stage Ad. The output signal Aed of thesecond stage Add is even more accurately representative of themass/density of the tested substance.

The principle of testing a substance (such as a tobacco rod) in order toascertain the moisture content is the same as described above inconnection with the determination of mass/density. The aforediscussedparameterization then involves resort to cigarettes having known butdifferent moisture contents. In other words, the weights of cigarettesare used in conjunction with a determination of density/mass, and themoisture contents are resorted to when the method and apparatus of theinvention are to ascertain the moisture content of successive incrementsof a running continuous cigarette rod.

An advantage of the method described hereinbefore with reference toFIGS. 11 to 13 is that the two values of the rectangular modulationoscillation can be more readily maintained in a stable condition than asinusoidal vibration. Additional advantages are achieved in connectionwith the evaluating signals which are generated as a result ofmodulation.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic and specific aspects of the aboveoutlined contribution to the art of ascertaining the characteristics oftobacco or other substances and, therefore, such adaptations should andare intended to be comprehended within the meaning and range ofequivalence of the appended claims.

What is claimed is:
 1. A method of ascertaining at least onecharacteristic of a substance by means of a high-frequency resonatorarrangement which is detuned in the presence of the substance,comprising the steps of supplying to an input of the resonatorarrangement microwaves having two different frequencies by repeatedlyshifting the frequency between high and lower frequency values, saidresonator arrangement being operable to produce first and second curvesof high-frequency output signals in the presence and absence of asubstance, respectively, said curves having different amplitudes at saiddifferent frequencies; and evaluating said output signals includingcomparing the amplitudes of at least said first curve at said differentfrequencies to ascertain the relative damping of said output signals atsaid different frequencies due to the presence of a substance to therebyascertain a characteristic of said substance.
 2. The method of claim 1,wherein said supplying step includes continuously transmitting to theinput microwaves having two different frequencies.
 3. The method ofclaim 1, further comprising the step of periodically varying thefrequencies of microwaves supplied to the input of the resonatorarrangement.
 4. The method of claim 3, wherein said varying stepincludes repeatedly and continuously wobbling between higher-frequencyand lower-frequency values.
 5. The method of claim 4, wherein saidmicrowaves have frequencies each allocated to a sloping flank of acurve.
 6. The method of claim 1, wherein the substance is tobacco andsaid at least one characteristic is the mass/density of tobacco.
 7. Themethod of claim 1, wherein the substance is tobacco in a tobaccoparticle flow and said at least one characteristic is the moisturecontent/mass of tobacco.
 8. The method of claim 1, wherein the substanceis tobacco in a flow of shredded tobacco particles and said at least onecharacteristic is the dielectric constant of shredded tobacco. 9.Apparatus for ascertaining at least one characteristic of a substance,comprising a resonator arrangement; means for supplying to an input ofsaid arrangement microwave signals at two different frequencies, saidarrangement having output means for the transmission of first and secondhigh-frequency output signals generated in the presence and in theabsence of a substance, respectively, at said arrangement; and means forevaluating said first high-frequency output signal at said two differentfrequencies, said evaluating means comprising means to mathematicallycombine said output signals at said two frequencies with constants togenerate signals representing a characteristic of said substance. 10.The apparatus of claim 9, wherein said supplying means includes at leastone microwave generator arranged to uninterruptedly transmit to saidinput microwave signals at said two different frequencies.
 11. Theapparatus of claim 10, wherein said generator includes means forperiodically altering the frequency of said microwave signals.
 12. Theapparatus of claim 9, wherein said supplying means comprises a microwavegenerator connected to said input and a frequency regulator connectedwith said generator to periodically vary the frequency of signals fromsaid generator between higher and lower values.
 13. The apparatus ofclaim 9, wherein said supplying means comprises a microwave generatorconnected to said input and a frequency regulator connected with saidgenerator to continuously and regularly vary the frequency of signalsfrom said generator between higher and lower values.
 14. The apparatusof claim 9, wherein said supplying means comprises a microwave generatorconnected to said input and a frequency regulator connected with saidgenerator to continuously and regularly vary the frequency of signalsfrom said generator between higher and lower values, said microwavesignals both being higher or lower than the resonance frequency of saidresonator arrangement.
 15. The apparatus of claim 9, wherein saidsupplying means includes means for transmitting to said input microwavesat frequencies having upper and lower threshold values and continuouslywobbling between said values, said values being at least substantiallysymmetrical with reference to an inversion point of a downwardly slopingflank of a resonance curve.
 16. The apparatus of claim 9, wherein saidsupplying means includes means for continuously transmitting to saidinput microwave signals at two different frequencies, and furthercomprising means for scaling down the high-frequency signals betweensaid output means and said evaluating means and means for selectivelyfiltering, between said scaling down means and said evaluating means,those frequency ranges which influence said shifts of resonancefrequencies and said damping of the resonance curves by a substance. 17.The apparatus of claim 9, wherein said arrangement comprises a metallichousing having an inlet and an outlet for a flow of a substance to betested, such as a tobacco stream.
 18. The apparatus of claim 17, whereinsaid housing is dynamically balanced.
 19. The apparatus of claim 18,wherein said housing includes a cylinder.
 20. The apparatus of claim 17,wherein said arrangement further comprises at least one dielectricresonator in said housing.
 21. The apparatus of claim 20, wherein saidat least one dielectric resonator provides a path for the advancement ofa substance between said inlet and said outlet.
 22. The apparatus ofclaim 21, wherein said arrangement further comprises a tubular guide forthe substance, said guide including portions at said inlet and saidoutlet.
 23. The apparatus of claim 22, wherein said guide extendsthrough said at least one dielectric resonator.
 24. The apparatus ofclaim 22, further comprising conductive sleeves surrounding said guidein the regions of said inlet and said outlet.
 25. The apparatus of claim24, wherein said sleeves contain a metallic material.
 26. The apparatusof claim 9, wherein said arrangement comprises two resonators eachreceiving microwave signals from said supplying means, one of whichtransmits said high-frequency signals, and the other of which transmitsto said evaluating means additional signals influenced by a referencesubstance to compensate for disturbances.
 27. The apparatus of claim 26,wherein said arrangement further comprises at least substantiallyidentical housings for said resonators.
 28. The apparatus of claim 9,wherein said at least one characteristic is density/mass of tobacco. 29.The apparatus of claim 9, wherein said at least one characteristic isthe moisture content of cut tobacco in a cigarette rod.
 30. Theapparatus of claim 9, wherein said at least one characteristic is thedielectric constant of cut tobacco, particularly in a cigarette rod. 31.A method of ascertaining at least one characteristic of a substance bymeans of a high-frequency resonator arrangement which is detuned in thepresence of the substance, comprising the steps of supplying to an inputof the resonator arrangement microwaves having two frequencies byrepeatedly shifting the frequency between higher and lower values, theresonator arrangement being operable to generate at an output first andsecond curves of high-frequency output signals in the presence andabsence of a substance, respectively, said output signals havingdifferent amplitudes at said two frequencies; and evaluating said outputsignals including providing a further signal denoting the sum of saidamplitudes, processing said further signal into a signal denoting theaverage of said amplitudes, providing an additional signal denoting thedifference between said amplitudes, and transmitting said further andadditional signals to calculating stages, and mathematically combiningsaid further and additional signal with constants in said calculatingstages to generate signals representing a characteristics of saidmaterial.
 32. The method of claim 31, further comprising the step ofperiodically varying the frequencies of microwaves supplied to the inputof the resonator arrangement, said varying step including repeatedlyswitching between higher and lower frequency values.
 33. The method ofclaim 31, further comprising the step of modulating the frequencies ofsaid microwaves with a lower-frequency rectangular a-c voltage.
 34. Themethod of claim 33, wherein said output signals are d-c signals and saidmodulated frequencies have maximum and minimum values, and furthercomprising the steps of ascertaining the d-c signals which aretransmitted by the output of the resonator arrangement at said minimumand maximum values of said modulated frequencies, and processing thethus ascertained maximal and minimal signals into evaluation signals.35. The method of claim 17, further comprising the step of ascertainingsaid constants by parameterization on the basis of to-be-ascertainedreference values of the substance.
 36. The method of claim 35, whereinsaid reference values include the density/mass, moisture content anddielectric constant.
 37. The method of claim 31, wherein said substanceis tobacco and said at least one characteristic is the mass/density oftobacco.
 38. The method of claim 37, wherein said substance is arod-like filler of cut tobacco.
 39. The method of claim 31, wherein saidsubstance is tobacco and said at least one characteristic is themoisture content of tobacco.
 40. The method of claim 39, wherein saidsubstance is a rod-like filler of cut tobacco.
 41. Apparatus forascertaining at least one characteristic of a substance, comprising aresonator arrangement; means for supplying to an input of saidarrangement microwave signals at two different frequencies, saidarrangement having output means for the transmission of high-frequencyoutput signals at said two frequencies generated in the presence of asubstance at said arrangement; and evaluating means for evaluating saidoutput signals, said evaluating means comprising summing and subtractingcircuits for summing and subtracting said output signals, to produce sumand difference signals, and calculating stages for mathematicallycombining said sum and difference signals, respectively, with constantsto determine first and second calculated output signals, and means foradding said calculated output signals.
 42. The apparatus of claim 41,wherein said supplying means comprises a microwave generator connectedto said input and a frequency regulator connected with said generator toperiodically vary the frequency of signals from said generator betweenhigher and lower values.
 43. The apparatus of claim 41, furthercomprising means for modulating the frequencies of microwaves with alower-frequency rectangular a-c voltage.
 44. The apparatus of claim 43,wherein the first and second high-frequency signals are d-c signals andthe modulated frequencies have maximum and minimum values, and furthercomprising means for ascertaining the d-c signals which are transmittedby the output means of the resonator arrangement at said minimum andmaximum values of said modulated frequencies, and means for evaluatingthe ascertained d-c signals into evaluation signals.
 45. The apparatusof claim 27, wherein said evaluating means further comprises means forascertaining said constants by parameterization on the basis ofreference values of a substance, said reference values including--as afunction of the at least one characteristic to be ascertained--at leastone of the density/mass, moisture content and dielectric constant of thesubstance.
 46. The apparatus of claim 41, wherein said resonatorarrangement comprises a metallic housing having an inlet and an outletfor the flow of a substance to be tested, such as a tobacco stream. 47.The apparatus of claim 46, wherein said housing is dynamically balanced.48. The apparatus of claim 47, wherein said housing includes a cylinder.49. The apparatus of claim 46, wherein said arrangement furthercomprises a least one dielectric resonator in said housing.
 50. Theapparatus of claim 41, wherein said at least one characteristic isdensity/mass of tobacco.
 51. The apparatus of claim 41, wherein said atleast one characteristic is the moisture content of cut tobacco in acigarette rod.